Mold clung to the ceiling and left dark trails across the walls and floor. The teacher had already complained about the stench months before.

Stuff was even growing on desks.

Classroom 103 at Walker Middle School in Orlando had become a breeding ground for mold. When an inspector investigated last year, he found the humidity at about 86 percent.

And this was no isolated incident.

Moldy classrooms and other indoor-air-quality issues have sparked thousands of complaints from teachers and students during the past three years, an Orlando Sentinel investigation has found. Mold has infested walls and ceilings, ruined books and furniture and, in some cases, led to the wholesale evacuation of children from classrooms.

The Sentinel reviewed thousands of maintenance work orders, school district reports and e-mails as well as independent environmental studies in Lake, Orange, Osceola, Seminole and Volusia counties from August 2007 to August 2010. The key findings:

•Different approaches to the problem from school district to school district with inconsistent record keeping. In some cases, maintenance workers were allowed to paint over water-damaged areas instead of removing them as recommended by the U.S. Environmental Protection Agency.

•Parents who are often kept in the dark about the problem.

For nine months a year, 2.6 million students and hundreds of thousands of teachers and other employees spend at least six hours a day in Florida's public schools. Yet there are no state laws governing how schools should monitor, detect and handle mold buildup and other indoor air-quality issues.

School districts are not required to tell anyone about the problem — not even the local health department — despite a growing body of knowledge that mold can be especially harmful to children. Some people show no outward reaction to mold. In others, however, it can cause sneezing, runny noses, breathing problems and respiratory infections, health experts say.

Mold was one reason why Jessy Hamilton quit his job as a social-studies teacher at Walker Middle School in August. He said he fought mold and respiratory infections for most of the six years he worked there.

The gray-black fungi first appeared in his portable classroom after the hurricanes of 2004. At one point, the entire ceiling was covered in mold, yet he had to hold classes there for eight weeks before his class could move into the media center temporarily, he said.

When Hamilton returned to the portable, the mold seemed to be gone. But it reappeared. Again and again.

"They would look at it and say, 'Ah, it is not as bad as it was,'" said Hamilton, who was eventually moved to another classroom, which he said also had mold. "They painted over it, which dumbfounds me to this day."

The principal could not be reached for comment after repeated attempts. But a spokesperson for the school district said his records do not reflect any health concerns related to mold.

The state knows how widespread schools' indoor air-quality problems are, records and interviews with school district officials show.

The Florida Department of Education has acknowledged that about half of schools are burdened with environmental issues. But it would be expensive to fix them — an estimated $70 million just to start, according to a legislative report written in 2004, the last time the state took a serious look at the issue.

Not only would repairs be pricey, Florida could be setting itself up for lawsuits if it identifies those problems, wrote the Senate analyst who compiled the report.

Central Florida school officialsinsist schools are safe. They said they urge their employees to report air-quality concerns immediately and that they respond as quickly and aggressively as they can.

Part of the problem, they said, is money. They need more of it — and more personnel — to make repairs, upgrade air-conditioning systems and search out water damage.

The state Legislature has slashed funding for such maintenance projects in the past several years.

School districts do not want it publicized that they have mold problems.

"There is often a greater desire to hide problems than have them resolved," wrote the UCF researchers who, in 2006, found that schools in Florida, Texas, New York and three other states had chronic problems with mold, humidity and odors.

In Orange County, school officials investigated about 1,200 complaints about indoor-air quality during the past three years.

Officials received about 50 complaints from Little River Elementary alone. They have been called to check out buildings dozens of times each at Brookshire and Pine Hills elementary schools and Cypress Creek, Dr. Phillips and University high schools.

Other schools with high numbers of complaints are South Lake High in Lake County, Indian Trails Middle in Seminole County, Gateway High in Osceola County and Deltona High in Volusia County.

Some of the damage has been significant, the Sentinel found.

For example, at Cypress Creek High in Orlando during the 2008-09 school year, inspectors found a 50-square-foot patch of ceiling that had water damage and mold in the boy's locker room. Older ceiling tiles infected with mold were being stored nearby.

In a neighboring mechanical room, there was standing water.

Brookshire Elementary in Winter Park reported late last year that a 32-square-foot section of ceiling in one of its portables had water damage and mold. Several days before, officials had visited to check out mold growing in patches in the media center and bleeding through the paint in a mechanical room. Two walls in a computer lab had blistering paint and mold.

Mold continually grows on the walls of a main interior hallway there — a problem the principal has complained about repeatedly.

The moisture and mold problems at Walker Middle, apparently caused by a leak that had gone unchecked, should have been reported sooner, said Zach Smith, an environmental coordinator for Orange schools. "Conditions inside classroom 103 likely did not develop over a short period of time," Smith wrote in his report.

When independent experts have tested the air inside local schools, they have found high levels of mold in about 40 percent of the cases. In some instances, they have discovered toxin-producing molds such as aspergillus and penicillium (which prompted city officials to shut down an Orlando fire station several months ago), and stachybotrys (a "black mold" that has forced the closure of numerous schools nationwide).

An environmental report from 2008, for example, shows that "aspergillus-penicillium" was found at Mill Creek Elementary in Osceola County. That August, the district spent more than $21,000 for an emergency cleanup of 35 classrooms there.

District officials throughout Central Florida said the number of complaints found by the Sentinel make the problem seem worse than it is. Teachers and other employees, they said, are not qualified to determine what is and is not mold with any accuracy.

In fact, a number of reports of "mold" turn out to be simply dark smudges of dust or dirt, officials said.

A "moldy" smell might actually be the unpleasant mixture of too many air fresheners in a room or odors from hamsters and other class pets, said Michael Corr, maintenance director for Lake County schools.

Corr also explained that sneezing, runny noses and headaches — typical allergic reactions to mold — can also be caused by factors such as strong cologne or pollen brought in from the playground.

"There are a lot of things in our everyday lives that can cause us to believe we have an indoor air-quality issue," he said.

Many of the complaints, however, prompted officials to take action — throwing out books, replacing ceiling tiles or cleaning air-conditioning systems and desks, tables and carpet. Some portable classrooms were recommended for permanent closure.

In some cases, however, districts did not perform cleanups as recommended by the U.S. Environmental Protection Agency and other experts. For instance, mold has been allowed to remain in place instead of being removed immediately. And workers do not always wear protective gear.

School employees said the situation might be worse than it appears on paper because some air-quality issues are never reported. A lot of teachers, in this poor economy, worry about losing their jobs or being retaliated against.

And employees are frustrated that some problems that are reported never seem to get resolved.

An Osceola County employee pleaded for help at Denn John Middle in Kissimmee in late 2008: "200 — whole building is molding. The classes, the halls. Please come and see for yourself. This is not a new problem. Only new students and parents to complain."

In a few parts of Florida, parents have spoken out about schools that seemed to make their youngsters sick.

Many times those districts did not make a concerted effort to fix problems until lawyers and the media got involved, said some of the parents who sued the Broward County school district over mold in 2003.

The State Attorney's Office in Broward investigated and brought its findings to a grand jury, which released a report criticizing school officials not only for dragging their feet on getting rid of mold but also for having schools so poorly constructed and maintained that they constantly leaked.

Broward spent millions of dollars on repairs, but a number of statewide changes the grand jury recommended never happened.

Richard J. Shaughnessy, director of The University of Tulsa Indoor Air Program and one of America's foremost air-quality experts, said the situation might not change unless the public pushes the issue.

"It has to start," Shaughnessy said, "with parents becoming involved and demanding that schools address these types of problems across the country."